1. Field of the Invention
The present invention relates to a semiconductor laser device and a method of manufacturing the same. More particularly, the present invention relates to a surface-emitting semiconductor laser device and a method of manufacturing the same.
2. Description of the Related Art
Recently, development of a surface-emitting laser array (also referred to as a VCSEL (Vertical Cavity Surface Emitting Laser) array) applicable to optical wiring between chips or boards and monolithically formed over a Si substrate has been proceeding.
For Si based Vertical-cavity light emitting devices, there is proposed a structure in which a silicon dioxide (SiO2) layer containing fine silicon germanium (SiGe) grains is used as a luminescent layer and the upper and lower sides of the luminescent layer are sandwiched between DBR (Distributed Bragg Reflector) mirrors composed of a multilayer film including a plurality of Si layers and SiO2 layers (see, e.g., K. Toshikiyo, et al., “Enhanced optical properties of Si1-xGex alloy nanocrystals in a planar microcavity”, J. Appl. Phys. 93, 2178 (2003)).
In a semiconductor laser device, a current (threshold current) for producing laser oscillation must be injected into a luminescent layer.
However, when a SiO2 film as an insulating film is used for the DBR mirror, it is impossible to form electrodes over top surfaces of the DBR mirrors sandwiching the luminescent layer and inject a current into the luminescent layer through the DBR mirrors. Therefore, an area of the luminescent layer is sufficiently made larger than that of the DBR mirror (cavity area) and an upper electrode is formed over a space of the top surface of the luminescent layer (see, e.g., Japanese Unexamined Patent Application Publication No. 10-256656 (paragraph number [0029] and FIG. 1)).
However, when the luminescent layer area is increased, a current per unit area (current density) injected into the luminescent layer is reduced and as a result, the laser oscillation cannot be created.
To increase the luminescent layer area to form an electrode structure on the layer, the luminescent layer area must generally be increased to be about 100 times as large as the cavity area. For example, assuming that a cavity diameter is 3 μm and an electrode width is 30 μm, the luminescent layer area required is at least 121 times as large as the cavity area.
Further, when the luminescent layer area is increased, a current flows concentratedly in a portion where an electrode is formed and as a result, in-plane dependency occurs in a luminescent portion in the luminescent layer as well as displacement may occur between a most light emitting portion and a portion where the cavity is formed.